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Journal of Bacteriology, December 2006, p. 8543-8550, Vol. 188, No. 24
0021-9193/06/$08.00+0     doi:10.1128/JB.01047-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Lysophosphatidylethanolamine Is a Substrate for the Short-Chain Alcohol Dehydrogenase SocA from Myxococcus xanthus{triangledown} ,{dagger}

Madhavi Avadhani,1 Roland Geyer,2,3 David C. White,2 and Lawrence J. Shimkets1*

Department of Microbiology, University of Georgia, Athens, Georgia 30602,1 Center for Biomarker Analysis and Department of Microbiology, University of Tennessee, Knoxville, Tennessee 37932-2575,2 Department of Environmental Microbiology, UFZ Leipzig-Halle, D-04318 Leipzig, Germany3

Received 18 July 2006/ Accepted 29 September 2006

Short-chain alcohol dehydrogenases (SCADHs) synthesize a variety of intercellular signals and other chemically diverse products. It is difficult to predict the substrate of a SCADH on the basis of amino acid sequence homology, as the substrates are not known for most SCADHs. In Myxococcus xanthus, the SCADH CsgA is responsible for C signaling during fruiting body development, although the mechanism is unclear. Overexpression of the SCADH SocA compensates for the lack of CsgA and restores development and C signaling in csgA mutants. The potential of SocA in generating the C signal enzymatically was explored by developing a dehydrogenase assay-based screen to purify the SocA substrate(s). A SocA substrate was extracted from M. xanthus cells with acidified ethyl acetate and sequentially purified by solid-phase extraction on silica gel and by reverse-phase high-performance liquid chromatography. The fraction with the highest SocA dehydrogenase activity contained the lysophospholipid 1-acyl 2-hydroxy-sn-glycerophosphoethanolamine (lyso-PE) as indicated by the fragment ions and a phosphatidylethanolamine-specific neutral loss scan following liquid chromatography coupled to mass spectrometry. The abundant lysophospholipid with the mass m/z 450 (molecular ion [M-H]–) had a monounsaturated acyl chain with 16 carbons. SocA oxidizes lyso-PE containing either saturated or unsaturated fatty acids but exhibits poor activity on L-{alpha}-glycerophosphorylethanolamine, suggesting that an acyl chain is important for activity. Of the five different head groups, only ethanolamine showed appreciable activity. The apparent Km and Vmax for lyso-PE 18:1 were 116 µM and 875 µmol min–1 mg–1, respectively. The catalytic efficiency (kcat/Km) was 1 x 108 M–1 s–1. The proposed product, 1-acyloxy-3-(2-aminoethylphosphatyl) acetone was unstable, and the fragmented products were unable to rescue csgA mutant development. The active fraction from thin-layer chromatography also contained an unidentified SocA substrate that had morphogenic properties.

* Corresponding author. Mailing address: Department of Microbiology, University of Georgia, Athens, GA 30602. Phone: (706) 542-2681. Fax: (706) 542-2674. E-mail: shimkets{at}uga.edu.

{triangledown} Published ahead of print on 6 October 2006.

{dagger} Dedicated to David C. White, 1929-2006.

Journal of Bacteriology, December 2006, p. 8543-8550, Vol. 188, No. 24
0021-9193/06/$08.00+0     doi:10.1128/JB.01047-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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